Poor sleep is a significant issue globally and impacts up to 60% of the adult population. The insufficient rest leads to underperformance at the work place. A tired person is also more likely to cause an accident, both in and outside of the workplace.
Sleep can be characterized by four distinct stages (phases) which change throughout the night. Sleepers move between the states, usually in an order.
There are typically several cycles of states (three to five a night) moving from NREM Stages 1 through 3 to REM, and then repeating. Each cycle lasts about 90-110 minutes. As it would be discussed later in the text, REM stage may be characterised by the so called Rapid Eye Movement of the user.
Stages 1-3 are known as non-REM (NREM) or quiet sleep. The new American Academy of Sleep Medicine guidelines groups NREM into three stages: N1, N2, and N3 (Iber et al. 2007). Usually a sleeper ascends from deep sleep briefly to light sleep before going into REM. These stages may be understood as follows:
Stage 1 (“N1”):                Transition between being awake and being asleep.        You lose awareness of your surroundings (feels like drowsiness when you are not completely awake), and can be easily woken from this state.        May experience generalized or localized muscle contraction associated with vivid visual imagery.        Sleep onset usually lasts 5-10 minutes.        
Stage 2 (“N2”):                Sleeping, but not particularly deeply (easy to wake from this stage).        Usually lasts 10-25 minutes at a time.        Typically, you spend about half the night sleeping in this state.        Your heart rate, breathing, and brain activity slows down in this sleep stage and your body completely relaxes        
Stages 3 (“N3”)—SWS, formerly known as stages 3&4 (Iber et al. 2007):                Deep, slow wave sleep (SWS). This is believed to be the time where your body renews and repairs itself.        After falling asleep it might take up to half an hour to reach this deepest part of your sleep. It takes far more effort to wake you up.        Your breathing becomes more regular, blood pressure falls, and pulse rate slows.        The amount of deep sleep varies with age (Dijk 2010).                    As you get older there is a decrease in deep sleep (and increase in lighter sleep).            You tend to sleep for a shorter length of time as you age. Therefore, you are more likely to wake up during the night as you get older (i.e., you are in light sleep for longer, from which you can more easily be disturbed by noise, movement of a bed partner, discomfort etc.). This is normal, and most older adults continue to enjoy their sleep.                        
Rapid Eye Movement (REM):                Your eyes move beneath closed lids, and you have most of your dreams. Your mind races, while your body is virtually paralyzed.        It is believed this stage facilitates learning and memory.        If you wake from this state, you tend to remember that you were dreaming. This can happen particularly as REM is followed by light sleep (i.e., starting a new cycle).        The first period of REM may only last 5 minutes or so, but progressively lasts longer over the course of a night, with the last period being up to 30 mins long.        REM sleep dominates in the final third of the night.        There are more changes in breathing pattern in REM as compared to slow wave sleep.        
Healthy Sleep
Healthy sleep is essential to a healthy life. Insufficient sleep for an extended period of time increases your risk for diabetes, obesity, depression, high blood pressure and even stroke.
Most healthy adults require 7-9 hours of sleep, with experts recommending 8 hours. Some people require only 6 hours, but others may require 10 hours of quality sleep. A University of California study from 2009 suggests that genetically some people can get by on 6 hours sleep—but this only applies to 3% of the population (O'Brien 2009). Most people experience difficulty getting to sleep or staying asleep at some point in their lives, particularly during times of stress or change. It is normal to have about 5% wakefulness during the night. All stages of sleep are important. However, a balance of deep, light and REM sleep is needed to feel at our best in the morning (Epstein & Mardon 2006).
A graph of sleep stages is referred to as a hypnogram (sometimes called ‘sleep architecture’ as the outline looks like the silhouette of a city skyline).
“Sleep Efficiency” provides a metric of how well a person has slept. This may be understood as working out the percentage of time spent in bed asleep each night. If a person spends 8 hours in bed, but only 4 of those hours are spent asleep, then the sleep efficiency may be very low at 50%. Sleep efficiency is based on the assumption that people go to bed in order to sleep.
Impacts on Sleep
A large number of publications have been dedicated to issues associated with sleep. Lack of sleep can affect important things like your personal relationships, productivity, and your overall mood. Lack of sleep can make people obese, and lead to health complications such as diabetes (Ostrow 2012; Patel 2006). If deep sleep is restricted, a person may wake up un-refreshed—no matter how long they have been in bed. It is believed that if you are sleep deprived, you tend to pass through light sleep rapidly to deep sleep, and spend more time in restorative deep sleep. If sleep is undisturbed after being deprived of REM sleep, a person will tend to enter REM earlier (and stay in this state for longer).
The literature notes that exercise is the only known way for an adult to increase the amount of deep sleep they get (Epstein & Mardon 2006).
Alcohol can make you drowsy and help you fall asleep, but suppresses REM sleep and is metabolised after a few hours so you may have more wakefulness.
It is thought that you can reach a point of severe tiredness where you no longer feel tired (but your decision making can be impaired). It may be possible to operate in this state, but your overall health could be affected.
Buysse et al. (2010) in “Can an improvement in sleep positively impact on health?”, Sleep Medicine Reviews 14, notes; “Reports from a large number of studies document significant associations between sleep duration and various health problems such as cardiovascular events, risk of stroke, incident artery calcification, changes in inflammatory markers and many more.” . . . “There is a need for more detailed investigation into long-term outcomes and the potential for causality.”
Åkerstedt et al. (2007) in “Sleep and sleepiness in relation to stress and displaced work hours”, Physiology & Behavior 92 notes: “Sleep is an important factor in relation to accidents, long-term health and mortality.” . . . . “We have also looked at the concept of sleep quality and found it dependent on sleep duration, sleep continuity and content of sleep stages 3 and 4. Sleep is also clearly disturbed in people on long-term sick leave for burnout or in individuals with high burnout scores, in particular sleep fragmentation is increased and sleep efficiency and sleep stages 3 and 4 (SWS—deep sleep) decreased.”
Dijk (2010), “Slow-wave sleep deficiency and enhancement: Implications for insomnia and its management”, The World Journal of Biological Psychiatry; 11(S1) notes: “An age-related decline in SWS and SWA (slow-wave activity) is well established. In some studies, apprehension, depression and insomnia have been associated with reductions in SWS and SWA. Experimental reductions of SWS through SWS deprivation (without altering total sleep time or REM duration) have been reported to lead to an increase in daytime sleep propensity and reductions in performance. SWS and SWA are therefore thought to contribute to the recovery processes that occur during sleep.”
Various methods of improving users sleep include physical exercise, breathing exercises and optimising the user's ambient conditions such as music, light, temperature etc. For example, the following approach may be taken to improve sleep:                1. Avoid caffeine at least four hours before bedtime as it can remain in the body for many hours.        2. Avoid smoking (or chewing tobacco) before bedtime and/or if you wake up during the night.        3. Avoid alcohol around bedtime; it may help you get to sleep, but it can also wake you up later in the night and disrupt REM sleep.        4. A light snack at bedtime may promote sleep—but avoid heavy meals. Foods containing high levels of tryptophan such as nuts, bananas, dairy, green leafy veg, eggs and soya products will promote good sleep.        5. Avoid vigorous exercise within two or so hours of bedtime (this may be subject dependent).        6. Keep your bedroom calm and comfortable, and at a comfortable temperature (e.g., between 65 deg F. and 75 deg F.).        7. Minimize noise and light in the bedroom; take advantage of light during the day—it will help regulate your body clock. Excessive light before bed may impact melatonin production.        8. Keep your bedroom mainly for sleeping and sex; try to avoid watching television, using your tablet or smartphone, listening to the radio, or eating in your bedroom.        
A Regular Sleep Schedule
Normally, people should try to maintain a regular sleep schedule. For instance, if a person stays up late on Friday, sleeps late on Saturday, they are set up to sleep even later on Saturday night. This can give rise to ‘Sunday night insomnia’.
In practice, this means trying to get up at the same time every day, even after a late night party. It also suggests that “sleeping in” at the weekend to make up sleep debt (Webster 2008) from the week may not be completely effective—especially if encountering ‘Sunday night insomnia’.
Insomnia
Insomnia means that the sleep problem is chronic (persisting for at least a month), and interferes with your day-to-day activities, perhaps through fatigue, irritability, or just a persistent feeling of being fed-up with things.
There are four main insomnia symptoms:                Problems getting to sleep        Problems staying asleep        Waking up too early in the morning (and unable to get back to sleep)        Not feeling refreshed in the morning        
Sleep deprivation can lead to:                Poor immune system        High blood pressure        Greater incidence of traffic and workplace accidents.        
Sleep Disordered Breathing
The term sleep-disordered breathing (SDB) can refer to conditions where apnoeas (e.g., cessation of airflow for ten seconds or more) and hypopnoeas (e.g., decrease in airflow that is at least 30% for 10 seconds or more with an associated oxygen desaturation or arousal) are present during sleep. It is estimated that one in every five adults has SDB (Young et al. 2002).
A variety of monitoring and sleep improvement products have been (or are) on the market, including wearable devices such as wristwatches, armbands, head mounted devices, and non-contact products. Examples of these are the following brands: Sleeptracker watch (monitors sleep stages throughout the night and uses that data to determine the exact moment when a person should be awoken helping the person feel refreshed and energetic), Lark (provides sleep assessment and coaching), Larklife (a product similar to Lark, but in the form of a wristband), Jawbone Up (wristband, tracks hours slept, light and deep sleep, time of awakening), Nike Fuelband (wristband, activity and sleep tracker), Bodymedia (armband, tracks duration and quality of sleep), Zeo (Headband Sleep Management System allows for creating a chart of the quality of the user's sleep patterns and provides a daily personalised assessment and expert advice), Omron Sleepdesign (wireless, a full picture of sleep health is provided, alongside a customized summary of health tips and advice), Gear 4 Renew Sleepclock (similar to Omron's Sleepdesign, +optimised wakeup).